The present application relates to the lighting arts. It finds particular application in conjunction with an LED-based light source, and will be described with particular reference thereto. However, it is to be appreciated that the present application is also amenable to other similar applications.
LEDs for high brightness systems are often surface mount devices soldered to metal core printed circuit boards (MCPCBs). The MCPCBs, which carry the LEDs, are attached in various ways to heatsinks or thermally conductive fixtures.
One common method of attachment of the board to the heatsink is by way of mechanical fasteners such as screws. However, where the heated components, e.g. LED boards, are clamped to the heatsinks with screws and insulating washers, it is common to experience a decrease in heat transfer efficacy over time. Long term creep or plastic deformation of the attachment might reduce the original clamping force to a fraction of the original value. This greatly compromises heat flow across the mounting interface, which may lead to thermally induced failure of the light source.
Another common method of attachment of the board to the heatsink is with an adhesive. Adhesive attachment systems are generally more resistant to high temperature operation, but sometimes exhibit detachment due to repeated temperature cycling. The relatively large differences in thermal expansion coefficients of plastics, epoxies and metals can give rise to substantial stress at the attachment region. Such stress may exceed the strength of the adhesive and may eventually result in the attachment failure.
Further inconveniences associated with attachment via mechanical fasteners and/or adhesives, is that each requires surface preparation and neither is well suited for easy detachment of the LEDs from the board.